JP2012513661A - Method for producing component layer for organic light emitting diode - Google Patents

Abstract

The present invention is a composition comprising at least one component material selected from the group consisting of a hole transport material, an electron transport material, a hole injection material, an electron injection material, and an emission material, a solvent, and a binder. The present invention relates to a method for preparing a constituent layer for an organic light emitting diode, comprising a step of grinding the product. It has been found that when grinding is used to prepare the dispersion or suspension, the resulting surface quality of the constituent layers is improved, thereby significantly improving the performance of the organic light emitting device. The present invention also provides an organic light emitting device including a constituent layer prepared by the above preparation method.
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Description

CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit of European Patent Application No. 08172712.5 filed on December 23, 2008, which is incorporated herein by reference.

  The present invention relates to a method for producing a constituent layer for an organic light emitting diode based on grinding. The present invention further relates to a light emitting device having a constituent layer prepared by such a method.

  Currently, various display devices, specifically those based on electroluminescence (EL) based on organic materials, are being actively researched and developed. Unlike photoluminescence (ie, emission of light from an active material due to light absorption and relaxation due to radioactive decay of an excited state), EL refers to the non-thermal generation of light caused by applying an electric field to a substrate. In the case of EL, excitation is achieved by recombination of opposite sign charge carriers (electrons and holes) injected into the organic semiconductor in the presence of an external circuit.

  Simple prototypes of organic light emitting diodes (OLEDs), or single layer OLEDs, generally consist of a thin film made from an active organic material sandwiched between two electrodes. One electrode needs to be translucent in order to observe the emission of light from the organic layer. In general, an indium tin oxide (ITO) coated glass substrate is used as the anode.

  In the case of producing a thin film from an active organic material, the deposition is mainly performed by a gas phase or liquid phase method. Vacuum deposition is used for small molecules and oligomers and is somewhat expensive due to the expensive equipment and low deposition throughput, but produces films with high field effect mobility and on / off ratio. Examples of organic material films deposited using this method are oligothiophene and oligofluorene derivatives, metallophthalocyanines, and acenes such as pentacene and tetracene.

  The vacuum deposition / patterning method widely used in OLED manufacturing methods is more expensive than solution methods such as printing, ink jet, and spin coating, and the manufacturing of large area glass panels larger than 17 inches is its manufacturing. Since the center of the large area glass panel is bent during the process, it is not appropriate. Accordingly, solution methods have been explored because they may overcome the above problems of vacuum deposition / patterning processes and increase device efficiency.

  Two forms of deposition are available for solution soluble organic semiconductors. That is, a soluble precursor of an organic semiconductor is deposited from solution and then subsequently converted to the final film or deposited directly from solution. The motivation for using soluble precursors is that the majority of conjugated oligomers and polymers are insoluble in common solvents unless they incorporate side chain substitution in their molecular structure. Adding side chains can interfere with molecular packing or reduce charge carrier mobility and increase π-π stacking distance between molecules, but if used properly, position rules As with the poly (3-hexylthiophene) (P3HT), it can be incorporated to enhance better molecular packing. However, it is difficult to determine the processing temperature because the conversion temperature from the precursor to the semiconductor is too high to be compatible with a low-cost plastic substrate. Furthermore, at least one additional processing step is necessary to convert the precursor to the corresponding semiconductor.

  Spin coating and solution casting are two common methods of direct solution deposition and are often used for polymers such as regioregular P3HT or various soluble oligomers. In addition, small molecules such as phthalocyanine-based materials have been used in wet methods such as spin coating and solvent casting techniques.

  U.S. Pat. Nos. 3,775,149, 4,371,642, 5,716,435, and 5,859,237, and WO 05 / 123844A1 are disclosed in US Pat. Various methods for producing pigments and dispersions such as phthalocyanines by milling or kneading using a bismuth are disclosed. For example, U.S. Pat. No. 3,775,149 describes a dispersion suspension of a crude pigment dissolved in an aqueous medium, preferably in an aqueous medium containing 5 to 10% surfactant until the pigment agglomerates. Disclosed is a process for preparing phthalocyanine pigments in the form of β-dyes to at least 80% by grinding with an insoluble particulate grinding component.

US 2001/009691 A and US Pat. No. 6,023,371 describe the fabrication of a display device that involves depositing an ink comprising a fluorescent dye and a host matrix by inkjet printing onto a substrate. Disclosed are methods and various fluorescent dyes and host matrices such as polymethylmethacrylate (PMMA), polybutadiene, and the like. US Pat. No. 6,087,196 also describes a method of forming a pattern on a substrate by depositing an organic material dissolved in a solvent by ink jet printing, and polyvinyl carbazole on the substrate by ink jet printing. Deposition of luminescent dyes dissolved in films and solvents, and methods for controlling the concentration of those solutions suitable for ink jet printing are disclosed. In US 2004 / 097101A, various materials such as copper phthalocyanine, tris- (8-hydroxyquinoline) aluminum (Alq ₃ ) are organically produced using solvent methods such as inkjet printing and spin coating. It is disclosed as a luminescent material for forming a layer.

  Other types of materials such as conductive materials are also being considered. U.S. Patent No. 6,366,017 and U.S. Patent Application Publication Nos. 2003 / 054579A, 2003 / 222250A, 2005 / 029932A, and 2007 / 031700A describe polyphenylene vinylene derivatives (e.g., , MEH-PPV), and various examples relating to the preparation of the emissive layer by spin coating of emissive materials and conducting polymers. However, these examples only make use of the release material, specifically the dissolution of the polymeric material in a solvent, and do not utilize grinding to prepare a solution / dispersion of the release material.

  Other patents such as JP 2007-157349A2, 2007-207591A2, 2007-207592A2, 2007-207593A2, and Chinese Patent Publication No. 1819303A are soluble. Disclosed are organic light emitting diodes and their constituent layers of various structures obtained by dissolving materials (eg MEH-PPV) or by mixing conducting polymers and doping small molecules.

  However, preparation of suspensions or dispersions of small molecule organic materials is difficult and sometimes inappropriate for the preparation of high quality films for OLED devices. Therefore, it would be desirable to develop a method for preparing suspensions or dispersions that can meet all of the above requirements.

  The present invention relates to a method for preparing a constituent layer for an organic light emitting diode, which can improve the surface quality of the resulting layer as described below.

  The present invention is a composition comprising at least one component material selected from the group consisting of a hole transport material, an electron transport material, a hole injection material, an electron injection material, and an emission material, a solvent, and a binder. Provided is a method for preparing a component layer for an organic light emitting diode, which involves grinding the object.

It is sectional drawing of the display apparatus containing the organic light emitting element of this invention. It is a front view of a paint stirrer. It is the schematic which shows the spin application process using the dispersion liquid of this invention.

Specifically, the present invention specifically includes: (a) at least one organic constituent material selected from the group consisting of a hole transport material, an electron transport material, a hole injection material, an electron injection material, and an emission material;
Crushing a composition comprising (b) a solvent, and (c) a binder,
The above grinding
(I) First, the binder is ground with a solvent,
(Ii) A method for preparing a constituent layer for an organic light emitting diode, which is performed in at least two steps of adding a constituent material.

  In one embodiment of the invention, the constituent materials are added to the mixture resulting from step (i) while continuing to grind. In the first embodiment, the pulverization is performed by (a) firstly binding the binder in a solvent in the presence of a pulverization medium, and (b) while continuing the pulverization, This is performed in at least two steps by adding at least one constituent material selected from the group consisting of a hole injecting material, an electron injecting material, and an emitting material.

  In another embodiment, the milling performed in step (i) is stopped, the constituent materials are added to the milled mixture of step (i), and the resulting mixture is further milled. In the second embodiment, pulverization is performed by (a) first pulverizing the binder in a solvent in the presence of a pulverization medium, (b) adding at least one constituent material to form a mixture, Next, (c) the resulting mixture is further pulverized in at least three steps.

  In some specific embodiments, after steps (i) and (ii), an additional step of diluting and repeating the milling can be performed until the viscosity of the milled mixture is in the range of about 1 to about 50 cp.

  In another embodiment of the invention, the step of diluting and repeating the pulverization is further performed until the viscosity of the pulverized mixture is suitable for spin coating, and the mixture is spin coated to prepare the constituent layers.

  In the present invention, the constituent material is preferably an organic constituent material.

  The binder is preferably selected from materials that do not lose fluorescence, particularly materials that can be finely patterned by screen printing, photographic engraving, and the like. In a preferred embodiment of the present invention, the binder is a polymer material, specifically a conductive polymer material, more specifically a vinyl group such as poly (vinyl butyral), poly (ethylene glycol), etc. Poly (sulfone) containing phthalic acid groups such as poly (ethylene terephthalate) containing poly (methyl methacrylate), poly (acrylate), poly (acrylonitrile) and other acrylic acid groups ), Polymers made from monomers containing conjugated double bonds, containing styrene groups such as poly (styrene-co-butadiene), containing sulfide groups such as poly (1,4-phenylsulfide), and these A polymer selected from the group consisting of a mixture, a copolymer thereof, and a mixture thereof.

  With respect to the solvent, the organic solvent used herein can be selected from well-known suitable organic solvents depending on the binder used and the constituent materials dissolved therein. For example, halogenated solvents such as monochlorobenzene, methylene dichloride, ethylene dichloride, 1,2-dichlorobenzene, and tetrachloromethane, heterocyclic solvents such as dioxolane and tetrahydrofuran, methanol, ethanol, propanol, octanol, Alcohols such as isopropyl alcohol and phenol; ketones such as cyclohexanone, methyl ethyl ketone, acetone, methyl isobutyl ketone, and N-methylpyrrolidone; acetates such as propylene glycol methyl ether acetate (PGMEA) and ethyl acetate; toluene and Aromatic solvents such as benzene, amines such as triethylamine, isopropylamine, and aniline, and charcoal such as hexane and cyclohexane It can be used and hydrogen, N, and amides, such as N'- dimethylformamide, and nitriles such as acetonitrile.

  Examples of constituent layers include a hole injection layer (HIL) containing a hole injection material (HIM), a hole transport layer (HTL) containing a hole transport material (HTM), and an emission layer containing an emission material (EM). (EML), an electron transport layer (ETL) containing an electron transport material (ETM), and an electron injection layer (EIL) containing an electron injection material (EIM). The emission layer or light-emitting layer has a function of injecting holes and electrons, transporting them, and recombining them to generate excitons (causing emission of light). A hole injection layer, sometimes called a charge injection layer, has the function of facilitating the injection of holes from the anode, while a hole transport layer, often called a charge transport layer, transports holes and electrons It has the function to obstruct the transportation of When the compound used for the light-emitting layer has a relatively low electron injection and transport function, an electron injection and transport layer having a function of facilitating the injection of electrons from the cathode, transporting electrons, and hindering hole transport Can be provided.

  With respect to the hole conducting emission layer, it can have an exciton blocking layer, in particular a hole blocking layer (HBL) between the emission layer and the electron transport layer. With respect to the electron-conducting emission layer, it can have an exciton blocking layer, in particular an electron blocking layer (EBL) between the emission layer and the hole transport layer. The emission layer also serves as a hole transport layer (in this case the exciton blocking layer is near or at the anode) or an electron transport layer (in this case the exciton blocking layer is near or at the cathode) It can also be fulfilled.

Some compounds used in certain constituent layers can work differently in other constituent layers of organic light emitting diodes depending on their work functions. For example, Alq ₃ is used as a green emitter, but it can be used in the electron transport layer simultaneously in some blue light emitting organic devices.

As the emission material, it is preferable to use a material having high fluorescence quantum efficiency and stability to both electrons and hole carriers. The release material is selected from the group consisting of (A) metal complexes, such as 8-hydroxyquinoline metal complexes and Ir complexes, (B) fluorescent organic dyes, such as hydrocarbons with fluorescent moieties, and (C) conductive polymers. There can be at least one type. Specifically, the Group A release material can be at least one selected from Alq ₃ or derivatives thereof (where q refers to 8-hydroxyquinolate and Ir complexes) and the Group B release The material can be at least one selected from 4,4′-bis (2,2-diphenyl-ethen-1-yl) diphenyl (DPVBi), coumarin 6, and perylene, and is a group C release The material can be at least one selected from polyphenylene vinylene, polythiophene, and derivatives thereof. For some release materials, additional purification steps such as vacuum sublimation can be performed to obtain better purity.

正孔輸送材料から作られる層は、有利には上記発光材料および（任意選択の）ホスト材料を含有する放出層中に正孔を輸送するために使用される。正孔輸送材料の例は、４，４’−ビス［Ｎ−（１−ナフチル）−Ｎ−フェニルアミノ］ビフェニル［「α−ＮＰＤ」］および４，４’，４−トリス［Ｎ−（１−ナフチル）−Ｎ−フェニルアミノ］トリフェニルアミン（ＴＮＡＴＡ）である。

正孔注入材料に関しては、正孔注入機能を有する任意の材料を使用することができる。具体的には正孔注入材料は、銅フタロシアニン（ＣｕＰｃ）、４，４’，４’’−トリス［３−メチルフェニル（フェニル）アミノ］トリフェニルアミン（ＭＴＤＡＴＡ）、および正孔輸送層にも使用することができる４，４’，４’’−トリス［Ｎ−（１−ナフチル）−Ｎ−フェニルアミノ］トリフェニルアミン（ＴＮＡＴＡ）から選択され、より具体的にはＣｕＰｃである。 A layer made of an electron transport material is preferably used to transport electrons into an emission layer containing a light emitting material and (optionally) a host material. A host material refers to a host matrix such as an inert polymer, such as polymethyl methacrylate (PMMA) or polybutadiene, that can be present in a hole or electron transport layer to form a layer. The electron transport material can be an electron transport matrix selected from the group consisting of metal quinoxolates (eg, Alq ₃ , Liq), oxadiazole, and triazole. An example of an electron transport material is tris- (8-hydroxyquinoline) aluminum of the formula [“Alq ₃ ”].

Layers made from hole transport materials are advantageously used to transport holes into the emission layer containing the light emitting material and (optional) host material. Examples of hole transport materials are 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl [“α-NPD”] and 4,4 ′, 4-tris [N- (1 -Naphthyl) -N-phenylamino] triphenylamine (TNATA).

With respect to the hole injection material, any material having a hole injection function can be used. Specifically, the hole injection material is also used for copper phthalocyanine (CuPc), 4,4 ′, 4 ″ -tris [3-methylphenyl (phenyl) amino] triphenylamine (MTDATA), and the hole transport layer. Selected from 4,4 ′, 4 ″ -tris [N- (1-naphthyl) -N-phenylamino] triphenylamine (TNATA), which can be used, more specifically CuPc.

Regarding the electron injection material, any material having such an electron injection function can be used. Specifically, the electron injection material can be selected from BaO, SrO, Li ₂ O, LiCl, LiF, MgF ₂ , MgO, and CaF ₂ .

  In another embodiment of the present invention, the composition further comprises CuPc, aromatic amine, distyrylarylene derivative (DSA), naphthalene, polythiophene and derivatives thereof, perylene and perylene derivatives, poly (p-phenylene vinylene) and derivatives thereof, It includes at least one compound selected from the group consisting of poly (9-vinylcarbazole) (PVK), oxadiazole and its derivatives, and triazole.

  Such an emission material, a hole transport material, an electron transport material, a hole injection material, and / or an electron injection material are preferably dispersed in a binder and an organic solvent described later. They should therefore be slightly soluble in the binder and the organic solvent. The proportion of binder and organic solvent in the release material is from about 1 to about 80% by volume, specifically from about 10 to about 60% by volume, more specifically from about 20 to about 40% by volume.

  For the preparation of emission materials, hole transport materials, electron transport materials, hole injection materials, and / or dispersions or suspensions of electron injection materials, milling is used in the present invention. Specifically, ball milling is preferably used in the presence of inorganic spheres such as zirconia spheres or glass spheres. The particle diameter of the inorganic sphere is generally 1 μm to 10 mm, specifically 5 μm to 5 mm, and most specifically 0.01 mm to 2.0 mm. The grinding can be performed in any suitable grinding device such as a paint stirrer. Grinding is performed at a temperature of about 0 to about 100 ° C., specifically about 20 to about 80 ° C., more specifically about 40 to about 50 ° C., most specifically about 10 ° C. at the reflux temperature of methylene dichloride. The time can be from about 12 minutes to about 12 hours, specifically about 1 to about 8 hours, most specifically about 2 to about 4 hours.

  After ball milling, the resulting dispersion or suspension is tested to determine if it is suitable for spin coating. Any conventional method can be used for the discrimination, but preferred methods include filter tests in which the dispersion or suspension is filtered through a microfilter, on ITO glass using the dispersion or suspension. Preliminary application to the surface, or measurement of its viscosity.

  For typical spin coating, the dispersion or suspension preferably has a viscosity of 1.0 to 50 cp, more preferably 5 to 25 cp, and most preferably 5 to 15 cp. The viscosity of the resulting dispersion or suspension can be adjusted by dilution with a suitable solvent and repeated grinding procedures.

  If the dispersion or suspension obtained by grinding and any subsequent procedures is suitable for the application method, it is applied onto a substrate, specifically an indium tin oxide (ITO) coated substrate, to form the constituent layers. Can be formed. Coating methods used herein include bar coating methods, roll coating methods such as gravure or reverse coating methods, doctor or knife methods, nozzle coating methods, and spin coating methods, all of which are known in the art. Is known. In particular, the coating method used in this specification includes a spin coating method.

After the application process, the resulting constituent layer applied on the ITO glass prepared according to the present invention exhibits good surface quality as observed by scanning electron microscope (SEM) or atomic force microscope (AFM). Satisfying the requirements for manufacturing OLED elements. A multilayer structure of an OLED element having these constituent layers can be prepared. Specifically, this OLED has the multilayer structure shown in FIG. 1, 1 is a glass substrate, 2 is an ITO layer (anode), 3 is a HIL layer containing CuPc, 4 is NPD or 2- An HTL layer containing TNATA, 5 is an EML containing DPVBi and a binder, 6 is an ETL containing Alq ₃ , and 7 is an Al layer (cathode).

  Excellent results can be obtained based on the surface quality (for example, roughness) of the constituent layer obtained by the preparation method of the present invention, and the OLED device using the constituent layer of the present invention can be used in another method such as a vacuum deposition technique. It showed good performance over those with constituent layers prepared by the method.

  The invention also relates to a method of using the constituent layers of the invention for the production of OLEDs.

  Another aspect of the present invention relates to a component layer prepared by the method of the present invention, an OLED including the component layer, and a display device including the OLED.

Example 1
Copper phthalocyanine (CuPc), Alq ₃ , NPD, 2-TNATA, and DPVBi were purchased or synthesized by well-known methods and purified by sublimation performed in a sublimation apparatus. Brightness calculated from current / voltage / brightness characteristic lines obtained by EL / PL spectrophotometer for electroluminescence efficiency (measured in cd / A) and output efficiency (measured in Im / W) As a function of

1. Preparation of component dispersions Polyethylene glycol having a weight average molecular weight of 20,000 as a binder and tetrahydrofuran as a solvent were added to a polyethylene bottle containing zirconia beads having a particle size of 0.01 mm to 2.0 mm. . The first pulverization was performed in a paint stirrer for 2 to 4 hours, then purified copper phthalocyanine (CuPc) was added, and the second pulverization was further performed for 2 to 4 hours. A small amount of the mixture was withdrawn as a sample during the second grinding and its adaptability to the subsequent spin coating process was determined by a filter test using a microfilter. If the viscosity was too high (> 50 cp), an additional amount of solvent was added and the mixture was then milled for an additional 2 to 4 hours. Further, the particle size of the dispersion was measured by zeta potential. A dispersion of CuPc having a viscosity of 5-15 cp was obtained.

Alq ₃ , NPD, 2-TNATA, and DPVBi dispersions were also prepared in the same manner as the CuPc dispersion.

2. Spin coating for forming a constituent layer This CuPc dispersion was spin coated on ITO glass at a thickness of 0.1 to 0.2 μm. After the obtained layer was dried, the surface roughness of the coating film was observed by SEM or AFM.

An NPD layer was formed by spin coating onto the dried CuPc layer using an NPD dispersion (prepared above) followed by drying. DPVBi and Alq ₃ layers are sequentially formed on the NPD layer, and finally an aluminum layer is formed by vacuum deposition of aluminum to produce an OLED device having an ITO coated substrate / HIL / HTL / EM / ETL / aluminum layer did.

Comparative Example 1
A dispersion of copper phthalocyanine (CuPc) was prepared as in Example 1 except that polyethylene glycol, tetrahydrofuran, and copper phthalocyanine (CuPc) were added simultaneously. This dispersion was inferior in (dispersion) stability and could not be applied on the substrate due to sedimentation.

Comparative Example 2
An OLED is made as in Example 1 except that the hole transport layer (HTL) is formed by vacuum deposition of NPD. This OLED showed lower efficiency (about 33% lower) than that produced in Example 1.

Examples 2-5
The constituent layers were prepared as in Example 1 except that the following binders and solvents were used instead of polyethylene glycol and THF, respectively.

  The OLED elements prepared in Examples 2-5 showed performance comparable to that prepared in Example 1.

  It should be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Accordingly, this invention includes modifications and variations of this invention provided that they are within the scope of the appended claims and their equivalents.

Claims (11)

A method for preparing a constituent layer for an organic light emitting diode, comprising:
(A) at least one organic constituent material selected from the group consisting of a hole transport material, an electron transport material, a hole injection material, an electron injection material, and an emission material;
Crushing a composition comprising (b) a solvent, and (c) a binder,
Said grinding,
(I) first crushing the binder together with the solvent;
(Ii) adding the constituent materials;
A method that is performed in at least two steps.   The method of claim 1, wherein the constituent material is added to the mixture resulting from step (i) while continuing the grinding.   The method of claim 1, wherein the milling performed in step (i) is stopped, the constituent materials are added to the milled mixture of step (i), and the resulting mixture is further milled.   The method according to claim 1, further comprising the step of diluting with the solvent and repeating the grinding until the viscosity of the grinding mixture is 1 to 50 cp, preferably 5 to 25 cp.   5. The method of claim 4, further comprising the step of spin coating the milled mixture to prepare the constituent layers.   The binder is a polymer made from a monomer containing a vinyl group, an alcohol group, an acrylic acid group, a phthalic acid group, a sulfide group, a styrene group, or a conjugated double bond, and mixtures thereof, and copolymers thereof and The method according to any one of claims 1 to 5, which is a polymer material selected from the group consisting of:   The method according to any one of claims 1 to 6, wherein the pulverization is ball mill pulverization performed in the presence of zirconia spheres or glass spheres as a pulverization medium. The release material is at least one metal complex, preferably Alq ₃ and derivatives thereof (wherein, q is 8-hydroxy refers to a quinolate or Ir complex) is a metal complex selected from claims 1 to 7 The method according to any one of the above.   The emitting material is a fluorescent organic dye selected from at least one fluorescent organic dye, preferably 4,4′-bis (2,2-diphenyl-ethen-1-yl) diphenyl (DPVBi), coumarin 6 and perylene. The method according to any one of claims 1 to 7, which is a dye.   8. A method according to any one of the preceding claims, wherein the emissive material is at least one conductive polymer, preferably a conductive polymer selected from polyphenylene vinylene, polythiophene, and derivatives thereof.   The method according to claim 1, wherein the hole injection material is a phthalocyanine-based material, particularly copper phthalocyanine (CuPc).

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